Consecutive harsh winters in U.S. hammer hemlock-killing insect

March 9, 2015

By: WBIR

After one of the coldest months on record in East Tennessee, many people are more than ready for some warm weather. But the especially frigid winter has been a life-saver for some of the mightiest trees in the forest.

This winter’s sub-zero temperatures in the Great Smoky Mountains National Park have devastated the once unstoppable Hemlock Woolly Adelgid. The adelgid is an invasive insect from Asia that has killed millions of hemlock trees in the eastern United States. They first arrived in the Smokies in 2002.

“You know adelgids have been devastating in the Southeast,” said Jesse Webster, a biologist with the National Park Service who has coordinated the efforts to fight the adelgid in the Great Smoky Mountains. “We’re not just losing this one species of tree. We’re losing all of the associate species, the hundreds of species that rely on this tree.”

Scientists have worked non-stop to save any hemlocks they could. Their efforts are the reason many hemlocks are still alive at campgrounds and other locations in the Park as they were doomed for eradication as the adelgid flourished in the warm Tennessee climate. After more than a decade of taking it on the chin, the last two winters Mother Nature finally helped fight back with a stone-cold combination.

“We know the adelgids start to die when it reaches 3 degrees. We had the really long freeze in 2014 during the polar vortex with the temperature far below zero. That killed 80 to 90 percent of the adelgids in the park. Then this year we had another prolonged cold snap. One night it was -23 at the top of Mount LeConte. We believe that will result in another 80 to 90 percent mortality rate for any of the insects that survived last year. It is really going to help with Hemlock Woolly Adelgid control.”

While this winter’s cold weather has helped, in no way does it mean the Park is done fighting the adelgid. What it does mean is some of the other biological controls they’ve introduced to fight the adelgid have a better shot at success.

“Some of the beetles we introduced as predators for the adelgid, we’re now likely to achieve a balance between predator and prey a lot faster,” said Webster. “We also believe the extreme cold killed all of the adelgids at the higher elevations, so this year we can focus our treatments on stands of trees at elevations below 3,000 feet.”

But Webster is well-aware that populations of invasive species have a history of booms and busts. While the frigid winter has generated a welcome bust, a future boom is very possible.

“With their ability to reproduce exponentially we are always on guard against newer waves of killer adelgids,” said Webster. “The combination of the parks efforts and this little extra help from mother nature helps to ensure their will be hemlocks in the smokies for the next generation.”

While the last two winters were not a complete knockout, they have the adelgid on the ropes and give scientists a fresh start at fighting a devastating insect.”

“These cold temperatures have really just given us a leg up. It will be a real benefit to the hemlock in the Smokies.”

By: WBIR

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